THE EMISSION-SPECTRUM OF HELIUM HYDRIDE .5. CHARACTERIZATION OF LOW-LYING RYDBERG STATES (N=2-5)

The low-lying Rydberg states of helium hydride (n=2-5) are characterized. Absolute binding energies and quantum defects are derived from spectroscopic data. Isotope shifts and scaling of molecular constants with principal quantum number n are discussed. Comparison with available ab initio calculations shows good agreement. For nd states the transition from Hund's case (b) to (d) is treated. Their splitting is mainly caused by the quadrupole moment of HeH +. Some so far unassigned groups of spectral lines were shown to involve n=2-4 Rydberg states with vibrational excitation. © 1990 American Institute of Physics.